How can I write the vertices of a 2d polygon to a text file?
To keep it similar to what you have already scripted.

import bpy

current_obj = bpy.context.active_object
f = open("d:\\test.txt", 'w')  # use 'a' to append
for face in current_obj.data.polygons:
    for vert in face.vertices[:]:
        local_point = current_obj.data.vertices[vert].co
        world_point = current_obj.matrix_world * local_point
        f.write('x: %.2f\t y: %.2f\n' % (world_point.x, world_point.y))
f.close()